It isn’t easy playing mediator in the chest-thumping, Cold War time warp of U.S.-Cuba relations. It’s even harder to resolve Washington-Havana disputes in a way that pleases both sides. But Colombian President Juan Manuel Santos may well have performed that diplomatic feat this week when he defused a potential crisis at next month’s Summit of the Americas in Cartagena. Santos got Cuba to drop its request for an invitation to the gathering, thus assuring U.S. President Barack Obama will attend; but Santos, during a personal visit to Cuban President Raúl Castro on Wednesday, also promised to make Cuba’s exclusion a “high-level” summit topic, thus averting a possible summit boycott by leftist Latin American presidents.

The outcome further burnishes Santos’ growing reputation as a hemispheric interlocutor. “He’s definitely showing a certain capacity for regional leadership,” say Peter Hakim, emeritus president of the Inter-American Dialogue in Washington. “He’s set a good foundation for dealing with this issue.” Santos told Castro that as the Apr. 14-15 summit’s host, he can’t invite Cuba because “there isn’t [hemispheric] consensus” on letting the communist island take part in a gathering that, since its inception in 1994 (this is the sixth), is open only to democratically elected governments. That was a firm nod to the U.S., which considers Colombia its strongest ally in South America, if not all Latin America. But before leaving Havana Wednesday night, Santos stressed that “Colombia wants the Cuban situation discussed in a constructive and high-level manner” at Cartagena, with an eye toward including Cuba in the next summit.

Still, while both Washington and Havana could claim satisfaction, Santos may also have made this summit a more uncomfortable event for the two foes – and that’s a good thing, too. Hakim points out that because of Santos’ promise to put Cuba on the summit agenda – as well his recent calls to discuss drug legalization as a way of weakening narco-cartels, an idea the U.S. strongly opposes but which a growing number of Latin American presidents are starting to back – Obama may now also be dealing with the two issues that perhaps most separate the U.S. and Latin America. At the same time, making Cuba a high-profile subject at the summit may also mean putting that country’s dismal human rights record under a spotlight. That kind of negative publicity was a big reason Havana declined a recent invitation to rejoin the Organization of American States (OAS).

Santos’ Cuba conundrum, in fact, revolved around the question of how strongly linked the Summit of the Americas is to the OAS and its Inter-American Democratic Charter. The charter mandates that OAS member states adhere to democratic norms like multi-party elections and free speech. During the past decade, Cuba and its leftist allies in the region, led by Venezuelan President Hugo Chávez, argued that Cuba’s 1962 suspension from the OAS was a cold-war anachronism and should be rescinded, especially since right-wing dictatorships like Augusto Pinochet’s in Chile were never suspended. At a 2009 gathering of the 35 OAS members in Honduras, the body did vote to let Cuba back in – as long as a “dialogue” was held on improving the country’s human rights. Cuba, as a result, refused readmission.

But do the same criteria apply to Cuba’s participation in the Summit of the Americas? For the past 18 years it was assumed so; yet when Cuba again asked to attend the summit this year, the OAS surprisingly deferred to Colombia and Santos. Obama, facing re-election this year and knowing the U.S.’s politically potent Cuban-American leadership would crucify him for attending a summit alongside Castro, made it clear to Santos that he could not come if Cuba did. The Chávez-led bloc, known as the Bolivarian Alliance, or ALBA, likewise threatened to boycott the summit if Cuba was not invited.

Getting Castro to drop his request was key – and Santos probably could not have done that had he not already shown that he was a trustworthy broker. Since taking office in 2010, Santos has significantly reduced tensions between Colombia and ALBA neighbors like Cuba, Venezuela and Ecuador by moving Bogota in a more independent, less U.S.-dependent foreign policy direction. “Santos has played his cards very well,” says Ariel Armony, director of the University of Miami’s Center for Latin American Studies. “This more autonomous approach is helping Colombia emerge as a player alongside Brazil.” Santos’ visit this week to Cuba – the first by a Colombian President in 13 years – was also a smart touch that “let Raul feel he was getting some diplomatic advantage out of all this,” says Hakim.

The Obama Administration felt it had won too. But Santos’ diplomacy also reminds the U.S. that its Cuba policy, including its 50-year-old but utterly failed trade embargo against the island, is a Cold War relic that alienates not just the more radical ALBA nations, but also the rest of Latin America. Most of the region’s governments don’t like Cuba’s communist regime, but they view Washington’s hypocrisy – its robust relations with communist China, for example, yet its resolute isolation of Cuba – as a reflection of its historically imperious approach to the western hemisphere in general.

Likewise, while he thanked Castro for “not creating a problem” for the summit, Santos also reminded Cuba that it can’t shirk its own problem of jailed dissidents and one-party rule. Whether or not Washington and Havana take all that to heart – and don’t get your hopes up – it was at least heartening to see a leader for once enter the time warp and emerge triumphant instead of trampled.